Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface. The touch sensor panel can be positioned in front of a display screen so that the touch-sensitive surface covers the viewable area of the display screen. Touch screens can allow a user to make selections and move a cursor by simply touching the display screen via a finger or stylus. In general, the touch screen can recognize the touch and position of the touch on the display screen, and the computing system can interpret the touch and thereafter perform an action based on the touch event.
In some configurations, touch sensor panels can be implemented as an array of pixels formed by multiple drive lines (e.g. rows) crossing over multiple sense lines (e.g. columns), where the drive and sense lines are separated by a dielectric material. In some touch sensor panels, the row and column lines can be formed on different substrates. Such touch sensor panels can be expensive to manufacture, because processing must be performed on two different substrates. In addition, the use of two substrates can result in a thicker device. In other touch sensor panels, the drive and sense lines can be formed on the top and bottom sides of the same substrate. However, touch sensor panels having row and column lines formed on the bottom and top sides of a single substrate can also be expensive to manufacture, because thin-film processing steps must be performed on both sides of the glass substrate, which requires protective measures for the processed side while the other side is being processed.
To reduce the cost of manufacturing touch sensor panels and reduce the thickness of the panels, advanced touch sensor panels may include an array of co-planar single-layer touch sensors fabricated on a single side of a substrate. In this advanced configuration, the sense lines can be continuous and maintain their generally columnar shape, but the drive lines may need to be formed from discrete shapes (bricks) coupled in the border areas of the panel using thin connecting traces. For example, each drive line can be formed from a row of discrete bricks coupled together by thin connecting traces. However, as the size of the touch sensor panel increases, more rows of bricks are needed to maintain the sensing resolution of the panel. As a result, more connecting traces have to be squeezed into the limited amount of space between the columns of drive line bricks to connect each row. This may require the connecting traces to be made narrower, which result in an increase in the resistance of the traces. The resistance of the traces may be further increased due to the longer distance they have to traverse in a large touch sensor panel. As a result, the stimulating signal bandwidth may be reduced due to the increased time constant introduced by these narrower, higher resistance drive lines, causing the touch panel to be less sensitive and more non-uniform.